Gas turbines are designed for ever higher operating temperatures for increasing the efficiency. In this case, especially the components or constructional elements in the region of the combustor and also the rotor blades and stator blades of the subsequent turbine, including the remaining elements which delimit the hot gas passage, are exposed to exceptional thermal loads. In order to efficiently counteract the occurring thermal loads, on the one hand especially resistant materials, such as nickel-based alloys, can be used. On the other hand, additional measures must be adopted for cooling the constructional elements, wherein different cooling methods, such as film cooling or impingement cooling, are used.
U.S. Pat. No. B2-6,779,597 describes multistage impingement cooling structures in the case of constructional elements of gas turbines, in which structures a wall, the front side of which faces the hot gas passage, is correspondingly impingement cooled on the rear side by means of perpendicularly impinging cooling air jets which are created by means of corresponding impingement cooling holes. The cooling effect in this case is intensified by means of projecting posts or pins which are in a distributed arrangement on the rear side and enlarge the heat-dissipating surface and intensify turbulences in the cooling air flow. The distributions of the impingement cooling holes and pins in the surface are constant in this case. The diameters of the impingement cooling holes in this case correspond to the diameter of the pins at the base. The density of the holes is considerably lower than the density of the pins.
U.S. Pat. No. 4,719,748 describes impingement cooling in the transition pipe between the individual burners and the inlet of the subsequent turbine, in which cooling air jets, which are created by means of impingement cooling holes, are directed onto the rear side of the pipe walls. By variation of the hole size and/or of the distances between the holes and/or of the distances from the holes to the pipe wall, the cooling intensity is varied and adapted to the respective thermal load. Pins for improving the transfer of heat are not provided.
Particular importance is attached to the cooling of the stator blades in the first stages of the turbine, because in this region the highest temperatures in the gas turbine occur. U.S. Pat. No. B2-7,097,418 describes how the outer platform of a stator blade can be cooled in a particularly simple manner by means of two-stage impingement cooling, wherein in a first stage the region at the trailing edge of the blade is cooled, and then the cooling air which discharges there cools the platform at the leading edge in a second stage. In both stages, differently positioned and spaced impingement cooling holes (30, 38 in FIG. 3) are used. Pins are not used on the rear side of the platform base.
The variation of the impingement cooling holes for adapting to the varying thermal loads usually results in the necessary amount of cooling air also being altered. If more holes per area unit are used—with hole diameters remaining the same—the consumed amount of cooling air is also increased, which leads to a reduction of the efficiency of the machine.